templatefile/pkg/templater/files.go

package templater

import (
	"log"
	"path/filepath"
	"strconv"

	"bytes"
	encjson "encoding/json"
	"fmt"
	"os"
	"text/template"

	"github.com/hashicorp/hcl/v2"
	"github.com/hashicorp/hcl/v2/hclsyntax"
	"github.com/zclconf/go-cty/cty"
	ctyjson "github.com/zclconf/go-cty/cty/json"

	"forge.cadoles.com/pcaseiro/templatefile/pkg/utils"
)

type ConfigFile struct {
	Destination  string `form:"destination" json:"destination"` // Where do we write the configuration file
	Source       string `form:"source" json:"source"`           // The template file short name
	TemplateType string `json:"type"`                           // The template file type (hcl or gotemplate)
	Mode         string `form:"mod" json:"mode"`                // The configuration file final permissions (mode)
	Owner        string `json:"owner"`                          // The configuration file owner
	Service      string `json:"service"`                        // Service to restart after configuration generation
	Group        string `json:"group"`                          // The configuration file group owner
}

// Generate the configuration file from the template (hcl or json)
func (cf *ConfigFile) Generate(root string, templateDir string, values []byte) error {
	var template string
	dest := filepath.Join(root, cf.Destination)
	source := filepath.Join(templateDir, cf.Source)
	intMod, err := strconv.ParseInt(cf.Mode, 8, 64)
	if err != nil {
		return (err)
	}

	template, err = cf.ProcessTemplate(source, values)
	if err != nil {
		return fmt.Errorf("Process templates failed with error: %v", err)
	}
	dirname := filepath.Dir(dest)
	err = os.MkdirAll(dirname, os.FileMode(int(0700)))
	if err != nil {
		return fmt.Errorf("Process templates failed with error: %v", err)
	}
	err = os.WriteFile(dest, []byte(template), os.FileMode(intMod))
	if err != nil {
		return fmt.Errorf("Process templates failed with error: %v", err)
	}
	log.Printf("\tFile %s generated\n", dest)
	return nil
}

// Process the template with the provided values
func (cf *ConfigFile) ProcessTemplate(source string, values []byte) (string, error) {
	var result string
	var err error

	if cf.TemplateType == "hcl" {
		// The template is an hcl template so we call processHCLTemplate
		result, err = cf.processHCLTemplate(source, values)
		if err != nil {
			return "", fmt.Errorf("Process HCL template failed with error: %v", err)
		}
	} else if cf.TemplateType == "go" {
		// The template is a go template so we call processGoTemplate
		result, err = cf.processGoTemplate(source, values)
		if err != nil {
			return "", fmt.Errorf("Process GO template failed with error: %v", err)
		}
	}
	return result, nil
}

// The actual template processing for Go templates
func (cf *ConfigFile) processGoTemplate(file string, configValues []byte) (string, error) {

	// The JSON configuration
	var confData map[string]interface{}
	var res bytes.Buffer

	err := encjson.Unmarshal(configValues, &confData)
	utils.CheckErr(err)

	// Read the template
	data, err := os.ReadFile(file)
	utils.CheckErr(err)

	tpl, err := template.New("conf").Parse(string(data))
	utils.CheckErr(err)

	utils.CheckErr(tpl.Execute(&res, confData["Config"]))

	return res.String(), nil
}

// The actual template processing for HCL templates
func (cf *ConfigFile) processHCLTemplate(file string, config []byte) (string, error) {

	fct, err := os.ReadFile(file)
	utils.CheckErr(err)

	expr, diags := hclsyntax.ParseTemplate(fct, file, hcl.Pos{Line: 0, Column: 1})
	utils.CheckDiags(diags)

	// Retrieve values from JSON
	var varsVal cty.Value
	ctyType, err := ctyjson.ImpliedType(config)
	if err != nil {
		return "", err
		/* Maybe one day
		cexpr, diags := hclsyntax.ParseExpression(config, "", hcl.Pos{Line: 0, Column: 1})
		if diags.HasErrors() {
			panic(diags.Error())
		}
		varsVal, diags = cexpr.Value(&hcl.EvalContext{})
		fmt.Println(cexpr.Variables())
		checkDiags(diags)
		*/
	} else {
		varsVal, err = ctyjson.Unmarshal(config, ctyType)
		utils.CheckErr(err)
	}

	ctx := &hcl.EvalContext{
		Variables: varsVal.AsValueMap(),
	}

	for n := range ctx.Variables {
		if !hclsyntax.ValidIdentifier(n) {
			return "", fmt.Errorf("invalid template variable name %q: must start with a letter, followed by zero or more letters, digits, and underscores", n)
		}
	}

	for _, traversal := range expr.Variables() {
		root := traversal.RootName()
		if _, ok := ctx.Variables[root]; !ok {
			return "", fmt.Errorf("vars map does not contain key %q, referenced at %s", root, traversal[0].SourceRange())
		}
	}

	val, diags := expr.Value(ctx)
	if diags.HasErrors() {
		return "", diags
	}

	return val.AsString(), nil
}